Thomas Bushnell, BSG scripsit: > So what I heard was that you wanted to represent an instant of time as > an integer, with some determinate resolution, and then the predictable > fight about whether the integer should be denominated in milliseconds, > microseconds, or nanoseconds. Not at all. My proposal allows instants to be either exact or inexact rationals. The question is, if you add 1 to a instant, do you get an instant one second later (modulo leap seconds), or 1 ms later, or what? This is neither accuracy, precision, nor resolution, but a fourth notion which I will call scaling. When instants are integers, scaling and resolution are the same thing, but not so when instants are allowed to be non-integers. I originally proposed that the scaling be 1 ms; that is, that adding 1 to an instant gets you an instant 1 ms later. However, it seems that enough people find that confusing that I've now switched to a scaling of 1 s; that is, adding 1 to an instant gets you an instant representing the next second. Marc Feeley's arguments persuaded me to require inexact rationals as the representation of instants. However, in practice these are 64-bit floats, which means since the resolution varies with the distance of the instant from the epoch, we currently (41 years after the epoch) can get approximately 10^-5 resolution at best if an instant is a 64-bit float, and it will get worse as time goes on. So I have removed the recommendation to use inexact numbers. > An instant should be a *number *without any mandated statement of just > what kind of number it is. And, as I said, an interface that answers > questions like "what time is it now" has an accuracy as well, which > should be returned (and which is *not* the same thing as the precision > of some determinate resolution). There is no worry about precision at > all if you just return a number, and an accuracy value. Most clocks don't know their accuracy at all, never mind knowing their accuracy accurately. > Posix decided that leap seconds were impossible, and now we have > the confusing rule that the epoch changes every time a leap second is > issued. Ah, well, but at this point we're stuck with that bad decision, > and it would be best if Scheme conformed to it. +1 > The separate question of what broken-out times > should look like is one which I think we should handle by simply aping the > Posix rules, which is pretty much what the proposal on the table looks like. It's a mixture of Posix and ISO 8601. -- Man has no body distinct from his soul, John Cowan for that called body is a portion of the soul cowan@ccil.org discerned by the five senses, http://www.ccil.org/~cowan the chief inlets of the soul in this age. --William Blake _______________________________________________ Scheme-reports mailing list Scheme-reports@scheme-reports.org http://lists.scheme-reports.org/cgi-bin/mailman/listinfo/scheme-reports
